1. Field of the Invention
The present invention relates to a polymeric monofilament and to a felt fabricated therefrom.
2. Description of the Prior Art
Polymeric monofilaments, in general, are produced by an extrusion process as is well known in the art. A polymeric resin is melt-extruded by an extruder equipped with a monofilament die into continuous strands of molten monofilaments. The resulting monofilaments are immediately quenched in a waterbath to form solid monofilaments. Thereafter, the solid monofilaments are subjected to an orientation process, which includes one or more steps of alternatingly heat stretching and quenching procedures, in order to impart physical strength.
Woven endless belts for conveying and guiding products under manufacture, which are utilized in various industrial processes, are one group of numerous applications where polymeric monofilaments are used extensively. Many of such conveyer belt applications involve harsh chemical and temperature environments in which ordinary polymeric materials cannot withstand. Papermaking machine felts are examples of such applications.
A papermaking machine, in essence, is a device for sequentially removing water from the paper furnish. A typical papermaking-machine is divided into three sections: forming, wet-press, and dryer sections. In the forming section, the slurry of paper furnish and water is deposited on a forming grid and water is drained, leaving a paper web of about 75 weight percent water content. The resulting web is carried into the wet-press section on a felt (wet-press felt) and passed through one or more of nip presses to reduce the water content of the web to below about 65 weight percent. The web is then carried to the dryer section and dried by contacting hot dryer cylinders on a felt (dryer felt) to reduce the water content of the web to below about 8 weight percent.
Although the felts for different sections of papermaking machine must be designed and fabricated to meet specific needs essential to each section, the felts must possess the general characteristics of dimensional stability, resistance to chemical and thermal degradations, resistance to abrasion, resiliency and tenacity. Both metal and synthetic polymers have been used to fabricate the felts with varying degree of success. Metal fabric felts provide superior thermal characteristics, but are difficult to handle, have poor flexure resistance and are prone to chemical attack and corrosion. These disadvantageous characteristics of metal fabric felts led to a wide acceptance of fabric felts made from a variety of synthetic polymers such as polyolefins, polyamides and polyesters. However, such synthetic polymer felts also exhibit certain disadvantages. Polyolefin felts, for example, are dimensionally stable but have low thermal stability and are not resistant to the chemicals utilized in the papermaking process. Felts made from polyesters provide dimensional stability, and are resistant to abrasion and chemicals, but are prone to high temperature hydrolysis. Felts made from polyamides, such as nylon 6 and nylon 6,6, provide abrasion resistance, resiliency and tenacity, but do not have the required dimensional stability.
There are many commercially available specialized synthetic polymers that are useful for the felt application. Currently, one of the most widely used synthetic polymers to fabricate felts for papermaking machines are long-chain polyamides such as nylon 6/10 and nylon 6/12. The long-chain polyamides provide tenacity, resiliency and abrasion resistance as well as dimensional stability. Polyaryletherketone fabrics also have been utilized in the felt applications as disclosed in U.S. Pat. 4,359,501 to DiTullio. U.S. Pat. 4,159,618 to Sokaris discloses yarns fabricated from liquid-crystal polymers, such as aramides, that are useful in the manufacture of woven felts. Although these specialty polymer felts provide good properties that are required in the papermaking felt applications, the high cost of these specialty polymers precludes wide acceptance of such felts. Consequently, it is desirable to have less expensive polymeric materials that exhibit the required characteristics suitable for the felt application.